Fluid catalytic cracking is an important process used in petroleum refineries for converting heavy feed into lighter products namely gasoline, diesel and liquefied petroleum gas (LPG). Processing of heavy feeds is becoming more significant because of cost reasons. However, processing of heavy feeds is difficult because of higher amounts of Conradson Carbon Residue (CCR) and poisonous metals such as nickel and vanadium.
In general in the catalytic cracking process, metal trap agents are added to the catalyst during its manufacturing process as a part of catalyst formulation or added as separate additive particles, or added to feed during processing step to handle feed metals and get maximum liquid petroleum gas and propylene yield of 25 wt % and 10 wt % on fresh feed basis.
U.S. Pat. No. 5,846,402 discloses a single catalyst component system comprising ultra-stable Y (USY) zeolite (1-6 wt %), shape selective pentasil zeolite (8-25 wt %), bottom selective active material (0-8 wt %), rare earth component (0-1 wt %) and non-acidic components and binder (91-60 wt %). It is used for enhancing ethylene, liquid petroleum gas, propylene and other olefins of heavy hydrocarbon feed stock such as mixed vacuum gas oil, Visbreaker (VB) tar, solvent deasphalted oil and paraffinic vacuum gas oil. The metal tolerance of the catalyst system is tested with the metal level of vanadium of around 20,000 ppm. It enhances the yield of LPG, propylene and other olefins.
U.S. Pat. No. 5,380,690 discloses another single catalyst/component system comprising clay (0-70 wt %), inorganic oxides (5-99 wt %), zeolite (1-50 wt %). The zeolite in the catalyst is a mixture of 0-25 wt % of Rare Earth Exchanged Y (REY)/high Silica Y zeolite & 75-100 wt % of phosphorus and rare earth containing high silica zeolite having a structure of pentasil, for enhancing ethylene, propylene and other olefins production in the feedstock. The feedstock consists of vacuum oil (0.881 gm/cc). The performance of the catalyst system is evaluated without metals.
U.S. Pat. No. 7,375,256 describes a catalyst comprising of phosphorous and transition metal modified silica rich zeolite, wherein said transition metal is at least one element selected from the group consisting of Fe, Co, Ni, Cu, Zn, Mo and Mn having a structure of pentasil in a riser or a fluidized bed reactor. The catalyst composition increases the yield of ethylene, propylene and other olefins in the feed stock of vacuum gas oil (VGO) (0.873 gm/cc) & paraffin based atmospheric residual oil (0.896 gm/cc). The performance of the catalyst system is also evaluated without metals.
U.S. Pat. No. 7,691,768 discloses a catalyst mixture comprising ECAT (100%), ECAT (96%)+commercial additive (4%) (K-2000), ECAT (96%)+Commercial additive (4%) (Re2O36C). Further, it also contains 6% p/p of the rare earth precipitated into the zeolite. It was evaluated in the feedstock of Heavy Gas oil (HGO) having density—0.852 g/cm3) and RCR −0.43% p/p, for enhancing the yield of LPG and propylene in the feedstock. However, the patent does not mention about presence and tolerance with respect to any metals in the feedstocks.
Solid acidic catalyst described in U.S. Pat. No. 4,980,053, is selected from the group consisting of pentasil shape selective molecular sieves, Ultra-stable hydrogen Y sieves, and a mixture of Ultra-stable hydrogen Y sieves and pentasil shape selective molecular sieves. It comprises of CHO-Pentasil+REY, ZCO-USY, CHP-Pentasil shape selective molecular sieve supported on kaolinite, and LWC II-amorphous alumino silicate catalyst used to increase the yield of ethylene and propylene. The feedstock for the catalyst includes vacuum gas oil VGO (0.873 gm/cc), Straight Run Naphtha (SRN), residual oil (RO). However, the presence of any metal on the catalyst is not mentioned.
U.S. Pat. No. 5,055,176 mentions a cracking catalyst comprising catalytically effective amounts of a large pore molecular sieve (5-50 wt %), a shape selective zeolite having paraffin cracking/isomerization activity (0.1-20 wt %), a shape selective zeolite having paraffin aromatization activity (0.1-20 wt %), and a matrix, used to increase ethylene and propylene. However, the metal tolerance of the catalyst is not disclosed.
U.S. Pat. No. 5,326,465 describes a solid acidic catalyst comprising rare-earth containing high silica zeolite having the structure of a 10-40% pentasil (ZRP), REY and high Silica Y zeolite which is used to crack the feedstock such as SRN, LGO, VGO and residues CCR (0.22-3.81) and for improving the yield of LPG, propylene and other olefins. The catalyst system is tested with metal containing only Nickel, but no vanadium.
In light of the prior art processes, there exist a need for developing a catalyst composition for maintaining a high LPG and propylene selectivity, such that the same can handle higher amounts of metal contaminants and higher CCR with high metal tolerance.